Re: [TLS] Mail regarding draft-ietf-tls-esni

Eric Rescorla <ekr@rtfm.com> Mon, 26 November 2018 22:44 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Mon, 26 Nov 2018 14:43:46 -0800
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To: Stephen Farrell <stephen.farrell@cs.tcd.ie>
Cc: njl@tlrmx.org, "<tls@ietf.org>" <tls@ietf.org>
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Subject: Re: [TLS] Mail regarding draft-ietf-tls-esni
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On Mon, Nov 26, 2018 at 2:08 PM Stephen Farrell <stephen.farrell@cs.tcd.ie>;
wrote:

>
>
> On 25/11/2018 17:18, Nick Lamb wrote:
> > In section 7.1 the -02 draft says:
> >
> >    Clearly, DNSSEC (if the client validates and hard fails) is a defense
> >    against this form of attack, but DoH/DPRIVE are also defenses against
> >    DNS attacks by attackers on the local network, which is a common case
> >    where SNI.
> >
> > Where SNI what?
>
> I'm guessing what's missing is an argument that DoT or DoH can
> (if better than opportunistic) counter some local attacks that'd be
> similarly mitigated by DNSSEC.
>

Actually, these local attacks are better mitigated by DoH/DoT, because
what you want is to conceal the name you are looking up.

-Ekr



> I'd be tempted to just say that yes, an active adversary can force you
> > to choose between privacy and connectivity, and hard fail DNSSEC is the
> > only existing way to choose privacy.
>
> Perhaps (exceptionally) less so in this case. The client here
> depends on confidentiality of the DNS query for both the A/AAAA
> and ESNIKeys RR's, so an authenticated DoT or DoH connection
> to a chosen recursive could be a pretty good defence here. And
> DNSSEC alone (hard fail or not) isn't sufficient.
>
> > The current text feels more like an attempt by people who don't want to
> > face the Dancing Pig problem to justify why their latest seat-belt that
> > snaps in a crash (to borrow Adam Langley's phrase) is a good idea
> > anyway. But regardless of whether I'm correct about that, the sentence
> > is confusing as it stands now.
>
> FWIW, I'd have no issue with more strongly encouraging DNSSEC,
> but I think ESNI turns out to be a situation where the presence
> or absence of DNSSEC perhaps makes less difference that in other
> TLS cases. For example, I think there's a stronger argument for
> DNSSEC being used to secure CAA RRs or those used by any ACME
> challenges, than there is for reasons related to ESNI.
>
> Cheers,
> S.
>
>
> >
> > Nick.
> >
> > _______________________________________________
> > TLS mailing list
> > TLS@ietf.org
> > https://www.ietf.org/mailman/listinfo/tls
> >
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>